The present invention relates in general to mineral mining installations and, more particularly, to hydraulic pressure fluid supply conduit systems designed for use in such installations.
It is well known to utilize a winning machine, such as a plough or shearer, which is moved back and forth along a mineral face in an underground working. A series of roof supports or chocks are usually arranged along the working and the mineral is transported away by a scraper-chain conveyor extending alongside the mineral face and conveniently supporting a guide for the winning machine. Each of the roof supports employs one or more hydraulic props which need to be set to brace the supports between the roof and floor of the working and relieved and/or retracted when the support is to be advanced. To advance the supports on the one hand and the conveyor and the winning machine on the other hand, double-acting hydraulic rams are connected between the supports and the conveyor. The shifting rams have to urge the conveyor and hence the winning machine against the mineral face with a certain force to produce the desired depth of cut. The various hydraulic appliances used in the installation and primarily the props and shifting rams need to be reliably supplied with pressure fluid to cause the appliances to operate.
In its simplest form, a hydraulic fluid conduit system would employ a pressure feed line or conduit connected selectively to the working chambers of the appliances to be charged with fluid and a return line or conduit connected selectively to the working chambers of the appliances to be evacuated. Normally, control valves or devices would be used to switch the connections between the feed and return lines and the appropriate working chambers of the appliances. Generally speaking, the hydraulic appliances operate under different operating conditions. For example, during shifting of the conveyor, one shifting ram may encounter a greater resistance to shifting than another ram. Similarly, one prop may need to be extended or retracted to a greater extent than another. The quantity of hydraulic pressure fluid drawn off from the feed line can thus very considerably from one appliance to another and regions of the feed line can be exposed to back pressure. As a result, different pressures can be established in the feed line over the length of the working and appliances such as the shifting rams may be charged with fluid at somewhat different pressure. One result of this problem is that the individual sections of the conveyor may be exposed to different forces when the shifting rams urge the conveyor and the machine against the mineral face. Consequently, it is not possible to maintain a reasonably constant depth of cut and the cut face cannot be held straight, as is desirable.
Once deviations occur in the face, problems occur, since the cutters of the machine can suddenly encounter high friction, which can cause fracture of the cutters or of components of the machine drive means.
A general object of the present invention is to provide an improved hydraulic fluid supply conduit system which will mitigate the problems mentioned.